Many proposals have been made previously for forming composite yarns and these generally divide into a number of categories. In one category the composite yarn is proposed to be formed at very high speed by false twisting the continuous filament strand and attempting to attach the fibres to this strand as it passes. No success has yet been obtained with a process of this type.
In a second category a continuous strand, generally a continuous filament yarn is introduced into a staple fibre spinning system at some convenient point. This has been done with ring spinning systems with some success, but with the disadvantage of very low speeds. It has also been tried with various forms of open-end spinning systems, particularly rotor spinning, vortex spinning, electrostatic spinning and friction spinning. However little success has been obtained to date.
Specific proposals on the use of this technique in friction spinning have been disclosed in U.K. patent specification Nos. 1 518 771 (Fehrer), 2 001 359-A (Barmag) and 2 011 956-A (VUB). In all cases a continuous strand is fed axially of the yarn so that the staple fibres wrap around the outside of the core to form the composite yarn. This technique is unsatisfactory in that the wrapping staple fibres are insufficiently connected to the core and can be stripped relatively easily. U.K. Patent Specification No. 2 001 359-A proposes the use of colloidal silica to overcome this problem, which does not get to the heart of the problem that the structure of the yarn is unsatisfactory.
Proposals in relation to the rotor spinning technique are disclosed in U.K. Patent Specification Nos. 1 154 554 (VUB) and 1 495 713 (SSI) and U.S. Patent No. 3,605,395 (Daiwa). In Daiwa and VUB the formed staple yarn is twisted around the continuous strand to form a composite yarn of corkscrew formation with the continuous filament unsatisfactorily on the surface. In SSI the core continuous filament is fed to the collecting groove of the rotor in a constant loop whereby it is absorbed into the centre of the staple strand and forms a yarn by the action of the untwisting false twist. This proposal has not achieved success presumably in view of the obvious technical difficulties and the unsatisfactory resultant yarn.
In relation to electrostatic and vortex open-end techniques, proposals have been made in U.S. Pat. Nos. 4,028,871 (Cor), 3,835,638 (U.S. Department of Agriculture), 2,817,947 (Strang) and in U.K. Pat. No. 1 373 255 (Goetzfried) in all of which the fibres are wrapped around an axial core of a continuous strand. Additionally Bobkowicz (various patents for example U.K. Pat. No. 1 569 110) has proposed bonding staple fibres to the outside of a continuous strand.
None of the above proposals utilizing open-end spinning techniques has been successful in that they do not form a satisfactory structure of a composite yarn. In all cases, either the continuous strand has formed the core around which the fibres are wrapped or alternatively the filament has been wrapped around a core of the fibres.